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Preparation And Characterization Of Hydrophobic Nanosilica

Posted on:2010-04-24Degree:MasterType:Thesis
Country:ChinaCandidate:Q ZhangFull Text:PDF
GTID:2121360275485413Subject:Materials science
Abstract/Summary:PDF Full Text Request
The development of the advanced and new technology makes request not only for the chemical composition of materials but for the morphology of materials. The research, production and thereof application of high-purified and ultrafine nanomaterials constitute an important part in the area of modem high technology. Silica,namely precipitate SiO2, has the characteristics of high purification, density, high specific surface area, well dispersion, and excellent optical and mechanical properties, so it has been used widely and become an important inorganic nanomaterial. The research on the preparation of nanosilica becomes a very important economic and practical work.Silica was prepared via the vitriol precipitation method using cheaper water glass as raw material. The influence of the reactant concentration (water glass, H2SO4, Na2SO4 ) and processing parameters (reaction temperature, stirring rate, solvent washing reaction) on the morphology and properties of silica were investigated systemically and optimized the synthesis technology. The structure, particle size and its distribution, and surface physical properties were also characterized.The FTIR and XRD analysis demonstrated that wadding-like nanosilica prepared in this work was amorphous SiO2. Although the primary nanosilica particle was spherical with the minimum size of 30~50nm, it is readily to contact with each other to form aggregates with average size of about 416.3 nm.As the ordinary nanosilica powder is hydrophilic inorganic compounds and have hydrophilic hydroxyl groups on its surface, it is readily to aggregate during the synthesis. The nanosilica is difficult to be dispersed uniformly within polymer matrix due to its bad affinity with inorganic polymer, which endows the composites with defect on the interfaces. In order to depress the aggregation of nanosilica during the preparation and improve the compatibility of nano-silica with polymer, the preparation of surface-hydrophobic nanosilica was also carried out and discussed.1. PEG6000 was used as surfactant to control the minienvironment for the coprecipitation reaction, in which the formed precipitates were bundled by PEG6000 and kept the precipitates from aggregating. The result showed that the average size of primary nanosilica particle was about 20~45nm, the average size of agglomerates was about 333.7nm, and DBP is 2.85ml·g-1 at the level of 2.0% PEG6000.2. Hydrophobic nanosilica was prepared by"one-step"precipitation method, that is, silane coupling agent KH570 was added into the reaction mixtures during the last stage of synthesis. The affinity of hydrophobic nanosilica with polymer matrix was expected to be improved. The activation coefficient of silica is 100%, the average size of primary silica particle is about 20~45nm, the average size of agglomerates was 264.8nm with narrow distribution, and DBP is 2.85ml·g-1 in the case of 2.0% silane coupling agent KH570, 1.5h of reaction time, and pH 4.7of solution3. The XRD indicated that the nanosilica was still amorphous non-crystalline structure after the treatment with surfactant PEG 6000 and silane coupling agent KH570.4. FTIR and TG analysis showed that the surface active agents PEG6000 and silane coupling agent KH570 is grafted to the surface of nanosilica by chemical bond rather than by simple physical adsorption. TEM photographs illustrated that the aggregation of nanosilica was improved significantly after the treatment with surfactant PEG6000 and silane coupling agent KH570.
Keywords/Search Tags:nano-silica, precipitation method, surface modification, hydrophilic
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